Poly(trimethylene arylate), particularly poly(trimethylene terephthalate) (also referred to as 3GT, Triexta or PTT), has recently received much attention as a fiber-forming polymer useful in textiles. PTT fibers have excellent physical and chemical properties. Continuous textured polyester yarns, prepared from partially oriented polyester yarns (POY) or spun drawn yarns (SDY), mostly polyethylene terephthalate (PET), are in wide-spread commercial use in many textile applications, such as knit and woven fabrics, as well as non-woven fabrics, such as spunbonded PET. The textile term “yarn” refers to a bundle of individual fibers. For example, shirts and blouses are often made from yarns made up of bundles of 30-40 filaments.
Polyester yarns, including both PET and PTT yarns, are prepared by a so-called melt spinning process, and are said to be “melt spun.” Melt spinning is a process whereby the polymer is melted and extruded through a hole in a so-called spinneret. In typical textile applications, the spinneret is provided with a plurality of holes, often 30-40, each about 0.25 mm in diameter. Multiple filaments are thereby extruded from a single spinneret. Those filaments are combined to form a bundle that is called a yarn.
Polyester yarns can be used in any combinations with or without other types of yarns. Thus, polyester yarns can make up an entire fabric, or constitute the warp, weft or fill, in a woven fabric; or as one of two or more yarns in a yarn blend, for instance, with cotton, wool, rayon, acetate, other polyesters, spandex and/or combinations thereof.
Fujimoto et al., U.S. Pat. No. 6,284,370, discloses a process for preparing 1-2 dpf PTT fibers wherein a first roll is heated to 30-80° C., a second roll is heated to 100-160° C., and the draw ratio imposed between the first and second rolls was is in the range of 1.3-4. In 13 examples and 11 counterexamples, Fujimoto never heated the first roll to a temperature above 60° C. except in one counterexample. In all the example, the first roll temperature was in the range of 50-60° C.
Ding, U.S. Pat. No. 7,785,507, discloses a process for preparing 2-3 dpf PTT fibers wherein a first godet is heated to 85-160° C., a second godet is heated to 125-195° C., and the draw ratio imposed between the first and second rolls was in the range of 1.1-2. Ding teaches that a first godet temperature of 75° C. caused excessive line breaks. Uster results were ca. 0.90-0.95%. In all the examples, the temperature of the first godet was 90° C. or more.
Howell et al., U.S. Pat. No. 6,287,688, describes preparation of textured PTT yarns that exhibit increased stretch, luxurious bulk and improved hand, as compared to PET yarns. Howell et al. describes preparing partially oriented PTT yarns at spinning speeds up to 2600 m/m. By contrast, PET is routinely melt spun at several times that speed. For reasons of cost, it is highly desirable to be able to spin PTT yarns at speeds higher than 2600 m/min.
Chang et al., U.S. Pat. No. 6,923,925, discloses a composition comprising PTT containing about 2% polystyrene (PS) that can be melt spun into spun drawn yarns at speeds up to 5000 m/min. Chang et al. is completely silent in regard to the denier uniformity (Denier CV) of the yarns so produced, and silent as well regarding the temperatures of the godet rolls employed for preparing the spun drawn yarn.
There is a need for a low denier spun-drawn filament yarn of PTT that can be spun at commercially viable spinning speeds and that is of sufficient denier uniformity to have practical utility in the preparation of high quality fabrics and garments.